One of the concerns in the manufacture of galvanic cells is that the space inside the cell be optimally utilized. Another concern is that the chemicals inside the cell should not creep through the sealed interface of the cell and leak out of the cell. Yet another concern is that foreign matter should not penetrate the cell through the seal.
The amount of chemicals inside the galvanic cell determines the electrochemical capacity of the cell, therefore it is important to utilize the space effectively. If for some reason the chemicals inside the cell leak, then that leakage may shorten cell life. This leakage can also cause a corrosive deposit to form on the exterior surface of the cell which detracts from the cell's appearance and marketability. Similarly, if foreign matter should enter the cell then such foreign matter may reduce the storage life and electrochemical capacity of the cell.
The chemical leakage which may reduce cell life can also cause corrosive deposits to form on the exterior surface of the cell. These corrosive salts may cause electrical discharge of the cell and may also damage the device in which the cell is housed. Usually the leaking chemical is the cell's electrolyte. This electrolyte leakage can occur in cell systems having aqueous or nonaqueous electrolytes, such as organic solvent-based electrolytes and liquid inorganic cathode-electrolytes, for example those based on thionyl chloride and sulfuryl chloride. Electrolytes such as alkaline electrolytes tend to wet metal surfaces and are known to creep through a sealed interface of a galvanic cell.
Generally, galvanic cells comprise a negative electrode, a positive electrode, a separator between said negative electrode and said positive electrode and an electrolyte solution in ionic contact with the negative and positive electrodes, all housed in a container and cover assembly provided with sealing means, such as a gasket, disposed between the container and cover assembly. The sealing gasket provides a primary barrier to electrolyte leakage. Much effort has been devoted to the design of sealing gaskets.
An example of a gasket disclosed in the art is shown in U.S. Pat. No. 4,457,990 (Gary R. Tucholski) in FIG. 5. The gasket has a peripheral flange and it sits within the container. A cover is then placed over the gasket such that the peripheral edge of the cover fits within the peripheral flange of the gasket. Thereafter, the top edge of the container is radially squeezed against the gasket flange and the cover edge. The top edge of the container is then crimped over the gasket to effectively seal the cover to the container. Because of the location and configuration of the gasket and the cover, less internal volume or space is available for active material. The gasket of this invention specifically addresses this problem and substantially increases the useable internal volume or space for the same external dimensions.
Consequently, it would be a substantial contribution to the art of galvanic cells to provide means for optimizing the space within the cell and to simultaneously provide an effective seal.
Therefore, it is an object of the present invention to provide a sealed galvanic cell wherein the internal volume of the cell is maximized such that a maximum amount of active materials is contained therein.
It is another object of the present invention to provide a substantially leakproof galvanic cell.
A further object of the invention is to provide a galvanic cell with a sealing gasket having a substantially U-shaped groove in each of its upper and lower surfaces.
Another object of this invention is to provide grooves of different cross-sectional shapes in a double-grooved gasket.
Yet another object of this invention is to provide grooves of different sizes in a double-grooved gasket.
The foregoing and additional objects of this invention will become apparent from the following description and accompanying drawings and examples.